How much does it cost to fix boiler error code AL 78?

Typical repair cost for the boiler AL 78 fault is £180-450 including labour.

AL 78 High

Boiler Fault Code AL 78

Also written as AL78 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code AL 78 appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected an internal electrical fault with the gas control system, meaning it cannot safely manage the fuel flow and has shut down as a precaution. (As reported on Sime Dewy 30/130 HE FS)

Pick your boiler brand for the AL 78 fix

Sime AL 78 6 models

Source

Information for the AL 78 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026